An example of such a power transmission device is described in Patent Literature 1. Patent Literature 1 relates to a lens tube of a camera capable of both automatic focus adjustment by an ultrasonic motor and manual focus adjustment by manual operation. The lens tube has an intermediate gear member between a driving member that is rotated by the ultrasonic motor and an operation member that is rotated by manual operation. Those components together form a planetary gear mechanism in which the intermediate gear member is a planetary gear, the driving member is a ring gear, and the operation member is a sun gear. The carrier of the intermediate gear member is connected to a lens driving tube which is a power receiving component.
In a lens tube having the above configuration, when the ultrasonic motor is driven or when the operation member is rotated, the intermediate gear member is rotated about the sun gear and, via the carrier, the lens driving tube is rotated, which enables focus adjustment.